Unmanaged, Managed, or Special Switch

[tutu]

we have a cause use 1768-43S CPU as a controller, with one 1768-ENBT as a Ethernet/IP interface.

does an unmanaged switch can handle both Safety (1791ES-xxx) modules and non safety (1794 Flex I/O) modules?

or it should be a managed switch or other special switch

 

[Timbert]

It doesn't matter. Use whatever is appropriate for your network layout.

The switch has no idea whether the data its transmitting is safety or standard IO, heck it could be a YouTube video of cats for all the switch cares.

All the information that makes Safety CIP 'safe' is embedded in regular old TCP/IP packets. The transmission medium is not required to be safe, in fact its assumed to be inherently unsafe. Safety is handled at the application layer not the physical or data link layers.

 

[James Mcquade]

i used managed switches only.

an unmanaged switch polls each port to see who wants to send / receive data. a managed switch waits for the signal and the sends / receives data accordingly. its fasster.

if there is little data, then it doesn't matter. if there's a lot of data, the managed switch is definitely the way to go.

regards,
james

 

[mellis]

James,

Do you have a reference to support the claim that managed switches are faster? I'd be interested to read about that.

My own basic (and potentially flawed) understanding of the difference is:
Unmanaged switch - Preconfigured, all ports are set the same. No I/P address for the switch.
Managed switch - Each port may be configured individually, allows VLANs. The switch requires it's own I/P address.

I expect an unmanaged switch with basic configuration to perform pretty much the same as an unmanaged switch. But I'm interested to learn more.

 

[The Plc Kid]

i used managed switches only.

an unmanaged switch polls each port to see who wants to send / receive data. a managed switch waits for the signal and the sends / receives data accordingly. its fasster.

if there is little data, then it doesn't matter. if there's a lot of data, the managed switch is definitely the way to go.

regards,
james

James,

Do you have a reference to support the claim that managed switches are faster? I'd be interested to read about that.

My own basic (and potentially flawed) understanding of the difference is:
Unmanaged switch - Preconfigured, all ports are set the same. No I/P address for the switch.
Managed switch - Each port may be configured individually, allows VLANs. The switch requires it's own I/P address.

I expect an unmanaged switch with basic configuration to perform pretty much the same as an unmanaged switch. But I'm interested to learn more.

As in most cases it depends. If we have 10 computers at layer 2 then given the same switch specs'procesor,OS,etc then they are about the same.


It really depends on the kind of traffic. If mostly unicast traffic then the speed would be about the same but throw a bunch of broadcast or multicast traffic on and the managed will be much faster at processing the traffic and keeping latency minimal.


You also need to define "speed". Link speed would be the same. packet speed from origin to destination could be much faster on the managed switch again depending on the type of traffic being sent.


The old advice of AC/DC drives applies here also. "always know thy load"


Managed switches are a must if the quality of the traffic matters also. Throw a VOIP phone system on a loaded network with no managed switches and I guarantee you will not like having a conversation with someone on that system.


It's comparing oranges and tangerines again. They are 2 very different kinds of switches for very different needs and applications.


"know thy load" and "know thy application"

 

[rdrast]

As above, it all depends on your infrastructure. As a matter of policy here, the 'uplink switch' on a line which connects to the plant network is managed, and set to filter multicast packets.

Any other switches on a line are unmanaged, but they only connect to line devices; never an external network.

Obviously, all of our main distribution switches (by area) are managed, as are the central core switches.

More and more we are moving away from unmanaged switches, but they do still have a place.

Hubs are shot on sight.

 

[rpoet]

Hubs are shot on sight.

Not that I disagree, but a hub still has a place in my toolkit if I have to Wireshark a device on a network and the switch can't support port mirroring.



-rpoet

 

[mellis]

The PLC Kid,

That's pretty much what I was thinking.

For unicast traffic, as long as the switch isn't swamped with traffic, I expect managed and unmanaged to perform the same. It's possible the unmanaged might even be a bit lower in latency just because it has less processing to do all else being equal.

Processing and blocking multicast and broadcast traffic in a managed switch requires more work to be done by the managed switch at that layer. More work means more latency. More powerful processors can offset this increased workload and keep the latency to a minimum. Where you see the benefit is that blocked traffic not being processed at all on the next layer.